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You suggest countries that have adopted a covid-19 elimination strategy will find it "difficult to reconcile their zero-covid border policies with those of countries learning to live... with the virus in some form" (Leader, 13 March). However, when vaccination is complete, borders will reopen, and the anguish and disruption seen in countries "learning to live …

Proposals to recycle carbon tax to citizens are flawed ( 20 March, p 44 ). The revenue is a limited-period source of money, which will be used to provide additional income that will become part of the core support mechanism for recipients and therefore politically difficult to switch off as carbon tax income declines to …

This article was fascinating and maybe alarming. Surely, if there is one black hole in the outer solar system there could be two? What if they collided? Would Earth bounce about like a ping-pong ball? Shouldn't we be told? Has anyone bought the film rights?

Your article on the role of the innate immune system in fighting infections suggests that the standard winter flu vaccine could significantly reduce the impact of covid-19 3 April, p 40 . In the UK, the winter flu vaccine is routinely offered to people over 60 or with underlying health conditions and yet it is …

In Graham Lawton's excellent article about innate immunity, the claim by researchers that mass influenza vaccination at the onset of the pandemic would have bought us time is reported. Convincing supporting evidence is cited from the health records of hospital staff in the Netherlands. There is a natural experiment waiting to be analysed in the …

Carlo Rovelli's contention that objects only exist when they interact with other things brought back memories of George Berkeley's theory of knowledge 13 March, p 36 . Berkeley's philosophy work led to the disturbing conclusion that objects would leap in and out of existence depending on whether or not they were being perceived. He overcame …

Alien planets should be safe from global warming as long as their economic system accounts for and costs out the consequential effects of their actions 10 April, p 12 . Sadly, although we reached the moon, our planet is in thrall to a hominin that seems incapable of counting beans.

In the preamble to the interview with Tanja Bosak, you say that if it were discovered that life had never gained a foothold on Mars, this would be deeply mysterious 10 April, p 46 . I don't think that it would be mysterious. What is mysterious is how life got started on Earth. As Bosak …

While the idea of developing new varieties of vanilla is interesting, it raises wider socio-economic and environmental issues 3 April, p 46 . Improving genetic diversity in this crop is to be applauded, but much of today's vanilla production occurs in relatively poor regions of the world where it is a valuable cash crop. Will …

Although there are still some detractors of the idea of a shift to hydrogen-powered vehicles, countries around the world are building infrastructure for this, with most major economies announcing hydrogen strategies 3 April, p 15 . Your article reports that such a move in the UK would be less efficient than a shift to just …